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There are six additional known HIV-2 groups, each having been found in just one person.
They all seem to derive from independent transmissions from sooty mangabeys to humans.
How the SIV virus would have transformed into HIV after infection of the hunter or bushmeat handler from the ape/monkey is still a matter of debate, although natural selection would favor any viruses capable of adjusting so that they could infect and reproduce in the T cells of a human host.
Since rural Africans were not keen to pursue agricultural practices in the jungle, they turned to non-domesticated meat as their primary source of protein.A study published in 2008, analyzing viral sequences recovered from a recently discovered biopsy made in Kinshasa, in 1960, along with previously known sequences, suggested a common ancestor between 18 (with central estimates varying between 19).Genetic recombination had earlier been thought to "seriously confound" such phylogenetic analysis, but later "work has suggested that recombination is not likely to systematically bias [results]", although recombination is "expected to increase variance".The majority of HIV researchers agree that HIV evolved at some point from the closely related simian immunodeficiency virus (SIV), and that SIV or HIV (post mutation) was transferred from non-human primates to humans in the recent past (as a type of zoonosis).Research in this area is conducted using molecular phylogenetics, comparing viral genomic sequences to determine relatedness.